1. Field of the Invention
This invention relates to an exhaust gas recirculation valve (hereinafter referred to as EGR valve) of an exhaust gas recirculation system (hereinafter referred to as EGR system).
2. Description of the Prior Art
An EGR system is intended for drawing exhaust gas in part into the combustion chamber of an engine by suction to cause the temperature of combustion of a fuel-air mixture in the combustion chamber to drop and at the same time to reduce the amount of NOx in the exhaust gas that might otherwise be emitted through the exhaust pipe. The EGR system is provided with an EGR valve for controlling the volume of exhaust gas to be introduced into the combustion chamber of the engine.
One type of EGR system with an EGR valve is disclosed in U.S. Pat. No. 3,762,384. Description of its construction and operation will be omitted.
The exhaust gas introduced into the combustion chamber contains moisture and fine carbon powders. One tendency inevitably shown by the carbon powders is that they find their way into a guide opening formed in a guide plate for guiding a valve stem having attached thereto a valve member for metering the exhaust gas. As a result, the carbon powders are deposited on the wall of the guide opening and the serious problem of the valve stem becoming fast on the guide plate due to the carbon deposition blocking the guide opening for the valve stem.